Cryogenic vibration sensor and insulator pad assembly, and cryogenic pumps including the same

ABSTRACT

A cryogenic-rated vibration sensor generally includes a cryogenic-rated accelerometer mounted to a top planar surface of an insulation block, wherein the insulation block includes a threaded opening on a bottom planar surface thereof for attachment to an object. Also disclosed are cryogenic pumps including the cryogenic-rated vibration sensor.

BACKGROUND

The present disclosure relates to vibration sensors for cryogenic pumpsand cryogenic pumps including the same.

Cryogenic pumps are centrifugal pumps designed specifically for handlingcryogenic fluids such as liquid natural gas (LNG), liquid petroleum gas(LPG), liquid ethylene, propylene, ethane, and like cold fluids. Thesepumps are oftentimes submersible and made to operate under extremeconditions compared to other process industries. For example, one of themore critical pieces of equipment in a liquid natural gas (LNG) terminalare the LNG pumps, which operates under cryogenic conditions of −161° C.

Depending on the particular application, these types of pumps may be ofsubstantial size with typical column lengths of about 15 to about 20feet (about 4.5 to about 6 meters) or more, and column diameters rangingup to about 3 feet (about 1 meter) or more. The pump is thus made up ofseveral major components, each of which may weigh several hundredpounds, wherein the total weight of the pump can be in excess of about10,000 to about 15,000 pounds (about 4,500 to about 6,800 kilograms) ormore.

Although the cryogenic pump is considered to be a quite reliable sincethe pump is normally installed in a clean, non-corrosive environment andis not exposed to the atmosphere, preventive maintenance of cryogenicpumps is often practiced since most cryogenic fluids have very highcontainment requirements to avoid gas leaks to the atmosphere or spills.Many pumps are now supplied with vibration detection systems. Thesesystems are normally in the form of an accelerometer mounted directly tothe pump housings with the instrument cable going up and out of thevessel or tank in much the same way as the power cables. These systemscan provide a vibration level for normal operation and can providealarms if vibration levels exceed an alert set point. The vibrationsystems can also be a valuable tool for trouble shooting, by allowingspectrum analysis of the vibration, which can be used to identify faultsor impending failure.

However, working in a cryogenic environment presents difficulties sincemany pump designs result in the vibration sensor being in exposed to thecryogenic conditions or in some cases parallel to the power cablesfeeding the pump motors contact with the flowing cryogenic liquid.Applicant has discovered that saturation of the accelerometer signalproduced by the vibration sensor can occur leading to inaccuratemonitoring even when employing a cryogenic-rated accelerometer.

BRIEF SUMMARY

These and other problems and deficiencies of the prior art are overcomeby providing a cryogenic pump including a suction pot including an inletat a lower portion; a head plate attached to a top of the suction port,wherein the cap includes a discharge outlet; a centrifugal pumpcomprising a vertically oriented pump shaft disposed within the suctionpot and suspended from the cap, wherein the pump is configured to move acryogenic fluid through the inlet to the discharge outlet; and at leastone vibration sensor mounted to a least one component of the cryogenicpump, wherein the at least one vibration sensor comprises an insulationblock having a bottom surface in direct contact with the at leastcomponent and an accelerometer coupled to a top surface of theinsulation block and free from direct contact with the at least one pumpcomponent.

The cryogenic-rated vibration sensor includes a cryogenic-ratedaccelerometer mounted to a top planar surface of an insulation block,wherein the insulation block includes a threaded opening on a bottomplanar surface thereof for attachment to an object.

The above described and other features are exemplified by the followingfigures and detailed description.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

These and other features will be described below with reference to thefollowing figures, in which:

FIG. (“FIG.”) 1 shows a side perspective view of an exemplary cryogenicpump in accordance with the present disclosure;

FIG. 2 depicts a top down view of the exemplary cryogenic pump of FIG.1;

FIG. 3 graphically illustrates rms velocity as a function of frequencyand time for an accelerometer mounted directly to a surface of acalibrated shaker;

FIG. 4 graphically illustrates rms velocity as a function of frequencyand time for the accelerometer mounted directly to the surface of thecalibrated shaker of FIG. 4, wherein an insulating block is positionedbetween the accelerometer and the surface;

FIG. 5 graphically illustrates rms velocity as a function of frequencyand time for an accelerometer mounted directly to a surface of acryogenic pump; and

FIG. 6 graphically illustrates rms velocity as a function of frequencyand time for the accelerometer mounted directly to the surface of thecryogenic pump of FIG. 5, wherein an insulating block is positionedbetween the accelerometer and the surface.

DETAILED DESCRIPTION

The present disclosure is generally directed to a vibration sensorconfigured for use with a cryogenic pump, wherein the sensor is attachedto a pump component of the cryogenic pump. As will be described ingreater detail below, the vibration sensor generally includes acryogenic-rated accelerometer attached to an insulator block, whereinthe insulator block is configured for attachment to the surface of adesired pump component. The vibration sensor in accordance with thepresent disclosure can be attached to any cryogenic pump surfaceundergoing rapid cool-down to cryogenic temperatures and be used toprovide accurate measurements. For example, after pumping cryogenicfluid such as liquefied hydrogen, liquefied nitrogen, liquefied naturalgas, or other cryogenic fluids having a temperature of between 0° K to125° K or more, some of the pump components and surfaces thereof will besignificantly chilled, wherein the vibration sensor can be attached tothe surface to monitor the pump vibrations during use and provide alarmsif the vibration levels exceed an alert set point.

Referring now to FIGS. 1 and 2, there is depicted an exemplary cryogenicpump 100. The exemplary cryogenic pump including the vibration sensor isnot intended to be limited to any particular type and/or configuration.By way of example, the cryogenic pump may be of a submersible-type, longshaft-type, vacuum housing-type, and the like, and commonly found in theproduction and transport of liquid natural gas (LNG), liquid nitrogen,liquid helium, and the like. As will be described herein, the vibrationsensor in accordance with the present disclosure can be mounted to anysurface of the cryogenic pump that undergoes rapid-cooling when pumpinga cryogenic fluid, wherein the vibration sensor accurately measuresvibration during operation thereof even when the surfaces reachcryogenic temperatures, i.e., temperatures less than 125 K. In mostembodiments, the vibration sensor will be disposed on a surfacegenerally parallel to the axial rotation of the pump shaft as will bedescribed below.

The exemplary cryogenic pump 100 includes a suction pot 110 primarilysupported by support ring 112 and support arms 114. Attached to the topof suction pot 110 is a cap 116 (also referred herein as the head plate)from which a centrifugal pump (not shown) is suspended within thesuction pot 110. Most centrifugal suction pumps generally include avertically suspended pump shaft, which carries at least one set ofvanes, which pumps the fluid by centripetal force in a known manner.During operation, inlet nozzle 118 is submerged into a liquid to bepumped or is fed pressurized liquid from one more feeder pumps (notshown), which then passes through one or more sets of the vanes (orimpellers), wherein each set of vanes constitutes a stage. At the top ofthe pumping chambers is an exhaust conduit 130, which passes the fluidto an exhaust outlet 132. In this manner, fluid enters from the bottom118 of the suction pot 110 and is discharged at an upper portion of thesuction pot 110 via the exhaust conduit 130. The pump shaft is driven byan electric motor to provide movement of the sets of vanes duringoperation. Power to the electric motor is provided by power cables fedthrough a conduit 122, which may include a breaker panel 124.

The illustrated cryogenic pump 100 may further include additional ventsand nozzles such as a seal vent port 134, a vent nozzle 126, afill/drain nozzle 128, upper and lower liquid level nozzles, variouspurge ports, and the like. The illustrated pump may further includeadditional vibration sensors without the insulation block, which can beexternally and/or internally positioned about the cryogenic pump.

A vibration sensor 140 in accordance with the present disclosure isshown coupled to the head plate 116 of the suction pot 110 and isutilized for detecting abnormal vibrations that could indicate a bearingfailure or other malfunction associated with the cryogenic pump.Although the vibration sensor is shown coupled to the head plate, otherlocations are contemplated, e.g., the suction pot, the pump casing, thebearing housing, and the like. Generally, it is preferred to provide alocation that is relatively accessible in the event repairs are needed,and/or at a location in close proximity to detect vibrations. Thevibration sensor 140 includes a cryogenic-rated accelerometer 142 and aninsulation block 144 intermediate the accelerometer and the cap surfaceas previously described. The insulator block can be attached to the capsurface using a stud and to the accelerometer with a second stud.Alternatively, an adhesive can be used. The cryogenic-ratedaccelerometer is a sensor, or transducer, which is designed to generatean electrical signal in response to acceleration (or deceleration) thatis applied perpendicular to the pump axis. Suitable cryogenic ratedaccelerometers are piezoelectric-based sensors commercially availableunder models series 351 from PCB Piezotronics, Inc.

The insulating block is not intended to be limited to any particularmaterial so long as the material is stable under cryogenic conditions.By way of example, the insulating block can be made ofpolytetrafluoroethylene, ultra-high molecular weight polyethylene,various thermoset plastic industrial laminates, G10 FR4 Glass epoxy, andthe like. The thickness of the insulating block is generally greaterthan 0.1 millimeter. The thickness is generally not limited so long as asignal can be detected. The insulating block is not intended to belimited to any particular shape and can be cylindrical, rectangular, orthe like. Generally, the insulating block has a planar top and bottomsurfaces to conform to the corresponding attachment surfaces of theaccelerometer and the pump component. The dimensions are generally equalto or larger than the surface defining the point of attachment of theaccelerometer to the insulating block. The dielectric constant is atleast 800 V/mil.

The thermoset plastic industrial laminates typically have a layeredconstruction with no fewer than two components. The first component is areinforcing substrate such as woven glass cloth, random glass mat, glassfilaments, woven canvas cotton fabric, woven linen cotton fabric, paper,woven aramid fabric, random mat aramid, woven graphite fabric, randommat graphite and others. The second component is a thermoset plasticresin binder which serves to adhere the layers of reinforcing substratesto each other to form a solid unit. Resin binders include epoxies,melamines, phenolics, polyesters, silicones and others. By way ofexample, a suitable thermoset plastic laminate is a NEMA grade G10 andFR4 glass-cloth reinforced epoxy. Representatively, the accelerometerportion 142 is a model series 351 quartz shear-structured cryogenicrated accelerometer sold by PCB Piezotronics, Inc., 3425 Walden Avenue,Depew, N.Y. 14043.

EXAMPLE

In this example, vibration was measured on a calibrated shaker and acryogenic pump using a cryogenic rated accelerometer with and withoutthe presence of the insulation block. The accelerometer was a groundisolated, cryogenic, quartz shear ICP® accelerometer, 100 mV/g, 1 to 2 kHz, 10-32 side connector (−320 to +250→F/−196 to +121→C), commerciallyavailable under the model number J351B41 from PCB Piezotronics, Inc. Theinsulation block was a cylindrical block made of G10-FR4, a continuouswoven glass fabric laminated with an epoxy resin, having a height of1.25 inch and a diameter of 1.25 inch. The insulation block included twothreaded holes to accommodate two studs: one between the block and studon the calibrated shaker or cryogenic pump and one between the block andaccelerometer. With regard to attachment to the cryogenic pump, thevibration sensor was attached to the cap in a location similar to thatshown in FIGS. 1 and 2. The cryogenic pump was a 13-stage high pressuresubmerged motor pump for liquid natural gas service and suction potmounted, which is commercially available from Nikkiso Cryo, Inc.

As shown in FIGS. 3 and 4, a comparison of room temperatureaccelerometer measurements produced by the vibration sensor on thecalibrated shaker demonstrated no alteration of the signal in thepresence and absence of the insulation block. This result indicates thatrms velocity as a function of frequency and time is substantiallyunchanged and that the insulation block did not interfere with signalintegrity to the accelerometer. However, when the vibration sensor wasused on a cryogenic pump in a cryogenic environment, wherein the skintemperature (i.e., surface) was as low as −256° F., the presence of theinsulation block between the accelerometer and the pump resulted in agood signal as shown in FIG. 5 whereas the absence of the insulationblock resulted in no usable signal as shown in FIG. 6 even though theaccelerometer was cryogenic-rated. Thus, the presence of the insulationblock effectively prevented saturation of the signal upon exposure thecryogenic temperature, i.e., the presence of the insulation blockprevented electromagnetic perturbations occurring in the accelerometer.Moreover, it is noted that the accelerometer was ground isolated, whichdid not affect the outcome.

While the disclosure has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the disclosure.Terms such as first and second as used herein are not intended to implyan order of importance or location, but merely to distinguish betweenone element and another of like kind. In addition, many modificationsmay be made to adapt a particular situation or material to the teachingsof the disclosure without departing from the essential scope thereof.Therefore, it is intended that the disclosure not be limited to theparticular embodiment disclosed as the best mode contemplated forcarrying out this disclosure, but that the disclosure will include allembodiments falling within the scope of the appended claims.

What is claimed is:
 1. A cryogenic pump comprising: a suction potincluding an inlet at a lower portion; a cap attached to a top of thesuction pot, wherein the cap includes a discharge outlet; a centrifugalpump comprising a vertically oriented pump shaft disposed within thesuction pot and suspended from the cap, wherein the pump is configuredto move a cryogenic fluid through the inlet to the discharge outlet; andat least one vibration sensor mounted to a least one component of thecryogenic pump, wherein the at least one vibration sensor comprises aninsulation block having a bottom surface in direct contact with the atleast one component and cryogenic rated accelerometer coupled to a topsurface of the insulation block and free from direct contact with the atleast one pump component, wherein the insulation block is adhesivelycoupled thereto or includes an opening configured to receive studs fromthe cryogenic accelerometer and/or the at least one component.
 2. Thecryogenic pump of claim 1, wherein the at least one component is thehead plate and the vibration sensor is mounted to the head plate and isparallel to axial rotation of the pump shaft.
 3. The cryogenic pump ofclaim 1, wherein the insulation block is a polytetrafluoroethylenematerial.
 4. The cryogenic pump of claim 1, wherein the insulation blockis a thermoset reinforced plastic comprising a reinforcing substrate anda thermoset resin binder.
 5. The cryogenic pump of claim 4, wherein thereinforcing substrate is selected from the group consisting of wovenglass cloth, random glass mat, glass filaments, woven canvas cottonfabric, woven linen cotton fabric, paper, woven aramid fabric, randommat aramid, woven graphite fabric, and random mat graphite and thethermoset resin binder is selected from epoxies, melamines, phenolics,polyesters, and silicones.
 6. The cryogenic pump of claim 1, wherein theinsulation block is a glass-cloth reinforced epoxy.
 7. The cryogenicpump of claim 1, further comprising additional vibration sensorsattached to other pump components, wherein the additional vibrationsensors are free of the insulation block.
 8. The cryogenic pump of claim1, wherein the insulation block has a thickness greater than 0.1millimeter.
 9. The cryogenic pump of claim 1, wherein the cryogenicrated accelerometer is a quartz shear-piezoelectric transducer.